Non-pneumatic tire

ABSTRACT

A non-pneumatic tire for a wheelchair or other wheeled apparatus includes an endless integrally molded solid core rubber tire with a tensile member embedded in the tire to minimize chance of roll-off of the tire from an associated rim. A method for producing the tire is disclosed.

BACKGROUND OF THE INVENTION

This invention relates to non-pneumatic tires for wheeled apparatus suchas wheelchairs, and particularly to an endless integrally molded tirefor such purposes.

Wheelchair tires have conventionally been produced from hollowcylindrical elastomeric extrusions. The pre-cured extrusion is cut tolength, fastened into a circle using a device similar to a hose barb,then machine stretched onto the rim. In a similar technique, a wire isloosely inserted in the hollow axial passage of the extrusion, and theextrusion and internal wire fastened into a circle by twisting orclenching the ends of the wire together, producing a joint at theabutting ends of the extrusion.

The above prior art wheelchair tires have suffered from certainproblems. A primary one is the relative ease with which the tireassembly is susceptible to rolling off the rim from side loadingencountered when turning the wheelchair sharply. This roll-off tendencyis believed attributable at least in part to the joint formed betweenabutting ends of the extrusion, and the fact that the wire insert hasfreedom of movement inside the extrusion, and is subject to breaking.Another problem is encountered by the wheelchair user when hiswheelchair tire needs replacement. It is generally necessary to have anew tire installed on the wheelchair using special machinery, oftentimesrequiring transport of the wheelchair back to the factory or repaircenter.

In another prior wheelchair tire configuration, an endless extrusionsurrounds an embedded or partially embedded coil spring located at theinternal diameter of the tire and whose ends are interconnected. Thetire may be snapped on and off an associated rim by hand. The coilspring, while aiding mounting and removal of the tire from the rim, willundergo unacceptably high elongation under side loading and thereforeresistance to roll-off is less than desired.

It is a primary object of the present invention to provide a snap-onendless integrally molded wheelchair tire which is resistant to roll-offeven under elevated side loading forces, and which can be easilyreplaced in the field.

SUMMARY OF THE INVENTION

Briefly described, in one aspect the invention pertains to anon-pneumatic tire for wheelchair or other wheeled apparatus comprisingan integrally molded endless elastomeric solid core element, and atensile member embedded in the interior of the solid core element andextending continuously throughout such interior.

In another aspect, the invention pertains to a method of making anendless, integrally molded wheelchair tire or tire for other wheeledapparatus including the steps of (1) forming a length of vulcanizableelastomeric material having a continuous longitudinal notch in one sidethereof; (2) positioning the length of material circumferentially aboutan endless fixture with the notch to the outside, and with the ends ofthe length in substantial abutting relationship; (3) placing a tensilemember in the notch with the tensile member extending continuously aboutsuch notch, to define a tire preform; and (4) inserting the tire preforminto a mold cavity and mold curing the preform to form an endless,integrally molded tire having a tensile member embedded therein.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the invention will be described withreference to the accompanying drawings, wherein like numerals designatelike parts in the several figures, and in which:

FIG. 1 is a partial perspective view of an endless tire and rim assemblyfor the rear wheel of a wheelchair according to the invention;

FIG. 2 is a cross-sectional view of an extrusion used in a preliminarystep in the production of the tire of the invention;

FIG. 3 is a view illustrating a secondary stage of building up the tire;

FIG. 4 depicts in cross section a partial view of a mold assembly usedin the production of the tire;

FIG. 5 illustrates an alternative embodiment of the tire of theinvention in cross section; and

FIG. 6 illustrates another alternative embodiment of the tire of theinvention shown in cross section.

PREFERRED EMBODIMENTS OF THE INVENTION

The invention will be described in particular with regard to a tire forthe rear (large) wheel of a wheelchair, and its method of production,however it will be understood that the invention also encompasseswheelchair front tires, and generally applies to non-pneumatic tires forvarious wheeled apparatus, such as carts, tricycles and other toys,hospital equipment, and horticultural equipment, such as lawn mowers andthe like.

Referring first to FIG. 1, there is shown a segmental portion of acircular wheelchair rim 10, supported by a plurality of radiallyextending spokes 12 leading to a central hub 11. The spokes are retainedon the rim by nuts (not shown) which protrude into the seating area ofthe rim. The channel-shaped rim is substantially semi-circular in crosssection, as shown.

Within the rim is seated the generally toroidal shaped tire 14 of theinvention. The tire is formed of a solid core elastomeric element 16 ofgenerally circular cross-sectional shape. The elastomeric solid coreelement is endless and integrally molded, and free from end-to-endjoints along the circumference of the tire. Although not narrowlycritical, it is preferred that the tire form a substantially conjugatefit with the adjacent sidewall surfaces of rim 10.

Tensile member or section 18 is embedded within the interior of thesolid core element and extends continuously through the interior of theelement in a circular fashion. As shown, the tensile section may beformed of a plurality of filaments, strands or cord members 20 formed ofa strain resisting tensile member, of textile or other material ofsufficiently high modulus to withstand the tension forces encountered inoperation together with a degree of extensibility to aid in mounting ofthe tire, to thereby hold the tire on the rim and resist rolling offwhile permitting ease of installation. Various tensile member materialsmay be employed, including without limitation polyester and nylon cord,oriented Hytrel (trademark identifying certain polyester thermoplasticelastomer compounds), cellulosic fibers such as rayon, and the like. Incertain applications substantially non-extensible material such as fiberglass or wire filament may be used, although in other applications anddepending upon placement of the tensile section, a degree of stretch ofthe tensile member may be desirable to assist in mounting the tire onthe rim. That degree of stretch, however, may in certain instances beprovided solely by the compression of the elastomeric body portion 22located intermediate the tensile section and the most radial inwardsurface of the tire element.

It is important that the aforementioned tensile section 18 be embeddedin the elastomeric matrix. In this manner, at least a portion of theouter surface of the individual tensile members is in intimate anddirect contact with the elastomeric material, resulting in a mechanicalcaptivation or bond, and/or chemical bond depending upon the relativenature of the materials and whether any bonding agent or treatment ispresent. In this respect the tensile member should be substantiallyspaced away from the radial innermost portion of the tire viacompression layer 22.

Although the cross section of the core element may be substantiallyround (as shown in phantom in the alternative embodiments of FIGS. 5 and6), it is preferred that the core element be provided with a continuousor semi-continuous notch 24 molded into the tire. The notch not onlyallows seating on the rim without interference with the aforementionedspoke retention nuts, but also may provide a resistance to rolling forceF, tending to roll the tire element off the rim. In this respect thesides 25 of the notch surface encounter the aforementioned nuts, whichlie along the inner surface of the rim, and limit further rollingmovement. This presumes a rolling action of the tire within the rim, asopposed to a pivoting action, which might occur depending upon therelative coefficients of friction and other factors.

In the alternative shown in FIG. 5, a single continuous tensile member18' is embedded in the elastomeric matrix 16 of the tire. This tensilemember may be formed of a rod of plastic or high modulus rubber stockwhose ends are fastened together, such as by heat fusing, curing toeffect cross-linking, or with the aid of a mechanical fastening device.Examples of suitable materials include polyester elastomer, polyethyleneor polyurethane rod.

Although not narrowly critical, it is highly preferred that the tensilesection 18 lie between the approximate cross centerline X--X of thetoroidal tire element and the radial innermost surface or notch 24 ofthe tire. Most preferably, in relation to cross centerline X--X (whichis normal to the plane of the tire and passes through the approximatecenter or centroid of the element), the tensile section center ispositioned at least 15 percent of the radial distance Y (see FIG. 5)below the centerline X--X, and more preferably at least about 40 percentof the radial distance Y below such centerline, and in either case atleast about 10 percent of the radial distance Y above the radialinnermost portion (24) of the tire.

However, in certain applications and depending upon the shape of thetire, it is satisfactory if the tensile section, such as 18" shown inFIG. 6, be at approximately the centroid of the element, or slightlythereabove. The important factor is to provide sufficient resistivetension to a rolling off force to offer sufficient resistance topreclude a total unseating of the tire from the rim. It may be tolerableif the tire deflects or lifts as long as it automatically snaps backinto the seating position.

The embodiment of FIG. 6 employs an asymmetrical tire shape to furthercombat the problem of wheelchair tire roll-off. In essence, by reducingthe radial extent Z of the core element radially outwardly of centerlineX--X, to be preferably less than the inward radial extent Y of the coreelement, the moment arm length and tendency for the tire to roll-off isreduced.

The tire of FIG. 1 is produced by building up the constituent materialsto form a preform, followed by mold forming the preform, utilizing heatand/or pressure as required. In the preferred method as partlyillustrated by reference to FIGS. 2-4, a continuous length ofvulcanizable elastomeric material 16' may be extruded, or molded to aparticular length, with a notch or other indentation 26 being providedin one side of the extrusion. The desired length of notched material isthen positioned circumferentially about endless fixture 29, which may beof the same cross-sectional shape as rim 10, for instance, with the endsof the length of elastomeric material brought into abutting relationshipat joint 30. Notch 26 is positioned away from the fixture so that itlies along the outer circumference.

A plurality of turns of tensile cord 20 are then wrapped about theelastomeric element so that the tensile section 18 (shown in phantom inFIG. 3) is positioned along the base or trough 28 of the notch, whichpreferably lies above the center of the element. It has been foundsatisfactory to wrap three turns of cord 20 about the notchedelastomeric element by starting at location 31, substantially oppositejoint 30, and proceeding clockwise for three turns and terminating at anoverlap position 32, also opposite joint 30. In certain cases, a singleturn of cord will suffice, preferably with an overlap provided.

The preform consisting of the endless rod-like elastomeric material,with radial outward notch and tensile member disposed therein, may thenbe flipped off or otherwise removed from fixture 29, principally becauseof the elasticity of the elastomeric stock and the positioning of thetensile member toward the outer portion of the preform. The preform isthen inserted in mold 34.

Mold 34 comprises identical mold halves 36, 38, within which ispositioned the preform blank. The preform is then mold formed in mold 34with the aid of heat and pressure so that the elastomeric materialsoftens and conforms to the shape of the mold surface (platens, sprueholes and other common features of the mold have been omitted from thedrawings.) With the preferred use of a heat shrinkable tensile member20, such as polyester cord, the heating encountered during the moldingoperation causes the tensile section to be displaced from its initialposition 40, corresponding to trough 28 of the preform, radiallyinwardly to the final location shown in FIG. 4. This radial displacementmay vary throughout the tire depending upon thermal shrinkagecharacteristics of the tensile and elastomeric body materials and otherfactors.

Upon demolding, the finished endless, integrally molded tire with fullyembedded tensile member is ready for mounting on rim 10, and this may beaccomplished simply by stretching the tire about the rim and snapping itinto place, much like mounting an automobile tire onto its rim. A handtool may be used as an aid depending upon the construction.

The elastomeric materials used for the tire should be selected orcompounded to fit the particular application, addressing such factors asresilience, durometer and compression set. Various natural and syntheticrubbers, such as polybutadiene, SBR, and polyisoprene and various blendsare suitable.

It is understood that the invention is capable of a variety ofmodifications and variations which will become apparent to those skilledin the art upon a reading of the present specification. The invention isintended to be limited in scope only according to the terms andequivalents in the appended claims.

What is claimed is:
 1. A non-pneumatic tire for a wheelchair or otherwheeled apparatus, comprising: an integrally molded endless non-jointedelastomeric solid core element; and at least one turn of astrain-resisting tensile member embedded in the interior of the solidcore element and spaced substantially from both the radial innermostextent of and sidewalls of the tire, and extending continuouslythroughout such interior, and the tensile member being sufficientlyextensible to permit snap-on mounting of the tire onto a channel-shapedrim.
 2. The tire of claim 1 wherein the tensile member is positionedmore closely to the radial inward surface of the tire than to thecircumferential (radial) outer surface of the tire.
 3. The tire of claim1 wherein the cross section of the tire is substantially circular, and aslot is positioned chordally along the radial inner surface of the tire.4. The tire of claim 1 wherein the cross section of the tire isasymmetrical with respect to a line drawn substantially through thecenter of the solid core element normal to a radial line of the tire. 5.The tire of claim 4 wherein the radial extent of the core elementradially inwardly of said line is greater than the radial extent of thecore element radially outwardly of said line.
 6. The tire of claim 1wherein the tensile member is formed of a plurality of turns of tensilecord in closely adjacent relationship.
 7. The combination of awheelchair wheel with the tire of claim 1 mounted thereon.
 8. The tireof claim 1 wherein the tensile member is located generally at thecentroid of the cross section of the tire.
 9. A one-piece wheelchairtire comprising: a generally circular cross-sectioned integrally moldednon-jointed endless elastomeric solid core element; a slot formed at theradial inward surface of the core element; and a continuousstrain-resisting tensile member embedded in the core elementintermediate the slot and approximate center of the core element,whereby the tire may be slightly stretched for installation onto a rim,while in use resisting roll-off encountered under side loading of therim mounted tire.
 10. The wheelchair tire of claim 9 wherein the tensilemember is integral with the core element and forms a bond with theelastomeric material of the core element.
 11. The wheelchair tire ofclaim 9 wherein the tensile member is positioned substantially adjacentthe slot near the radial inward surface of the tire.
 12. The wheelchairtire of claim 11 wherein the slot is mold formed into the core element.13. The wheelchair tire of claim 9 wherein the tensile member is formedof an endless plastic or rubber rod reinforcement, whose ends areattached together.
 14. The wheelchair tire of claim 9 in combinationwith an associated wheel having a hub, a rim, spokes connecting the rimconcentrically about the hub, and means disposed in the slot of the tiremounting the spokes to the rim.
 15. A non-pneumatic tire assembly for awheelchair or other wheeled apparatus, comprising:a channel-shaped rimhaving a radial innermost portion and lateral upstanding sidewallsurfaces terminating in outer edges; and a tire mounted on the rimcomprising:an integrally molded endless non-jointed elastomeric solidcore element seated between the sidewall surfaces; and at least one turnof a strain-resisting tensile member embedded in the interior of thesolid core element and spaced substantially from both the radialinnermost portion of the rim and said sidewall surfaces, and extendingcontinuously throughout such interior; said tensile member beingsufficiently extensible to permit snap-on mounting, and demounting ofthe tire from the rim while resisting roll-off while in assembled use onthe wheelchair or other wheeled apparatus.
 16. The tire assembly ofclaim 15 wherein at least a portion of the strain-resisting tensilemember is positioned radially inwardly from a straight line connectingthe respective outer edges of the sidewall rim surfaces.
 17. The tireassembly of claim 16 wherein the tensile member is in the form of aplurality of wound textile strands, filaments or cords formed in aclosely spaced fiber bundle.
 18. The tire assembly of claim 15 wherein aslot is positioned chordally at the radial innermost portion of the tireto form, with the rim, an annular void.
 19. A one-piece solid core tireadapted to be snapped on to a channel-shaped rim member, for use inwheeled apparatus comprising:an integrally molded endless andnon-jointed elastomeric solid core element of toroidal shape; and areinforcement integrally embedded interiorly within the solid coreelement and located near the center of the element cross section,extending throughout the interior of the element and spacedsubstantially from the lateral sides of the tire by interveningelastomeric material.
 20. The tire of claim 19 wherein the reinforcementis formed of a plurality of helical turns of a strain-resisting tensilemember positioned in adjacent proximity.
 21. The tire of claim 20wherein the reinforcement is bonded to the elastomeric material of thecore element.
 22. The tire of claim 19 in combination with an associatedone-piece rim having said channel shape with a radial innermost portionand lateral upstanding sidewall surfaces terminating in outer edges;said tire, in the form of a single endless member being mounted on therim so that the reinforcement is positioned radially below a straightline joining respective outer edges of the sidewall surfaces and isspaced farther from the sidewall surfaces than from the radial innermostportion of the rim.
 23. The tire of claim 22 wherein the reinforcementmember is in the form of a plurality of helically wound textile strands,filaments or cords formed in a closely spaced fiber bundle.